1. Field of the Invention
The present invention relates generally to data communication technology, and more particularly, to a method and apparatus for performing synchronization with respect to a device included in a data communication network.
2. Description of the Related Art
Due to the recent increased usage of smart phones, data traffic is rapidly increasing. The Korea Communications Commission has reported that the accelerated increase in usage of smart phones has caused a threefold increase mobile data traffic during the past year. It is expected that smart phone users will further increase usage of application services in their smart phones, which would increase traffic much further beyond the current traffic level. Especially, object intelligence communications that utilize objects, such as communications between a human and an object and communications between objects, which correspond to new mobile markets, are increasingly being performed in addition to previous communications between human beings. Accordingly, traffic transmitted to an evolved node B is expected to increase to a level that cannot be adequately supported with current infrastructures.
Therefore, there is a need for technologies capable of addressing such problems. One such technology, involves direct communication between devices in a mobile communication network. This technology, which is called Device-to-Device (D2D) communication, corresponds to a convergence between mobile communication technology and Machine-to-Machine (M2M) technology, which can increase the traffic capacity of an evolved node B and reduce overload of the evolved node B. The D2D communication refers to a communication in which User Equipments (UEs) within the same cell or cells adjacent to each other establish a D2D link between them and directly exchange data with each other through the D2D link, without passing the data through an evolved node B.
D2D communication schemes include a scheme that uses the same frequency as that used by an evolved node B and is performed either under the control of the evolved node B or while receiving support of the evolved node B, and a scheme that controls communication between UEs (devices), which use a frequency different from that of an evolved node B and independently perform D2D communications. The D2D scheme that involves controlling communication between devices requires a procedure for setting synchronization between the devices, and in such a scheme, the devices typically set synchronization between themselves by using time information received from a synchronous evolved node B or received through a Global Positioning System (GPS) reception module. However, when the devices set synchronization between themselves by using time information received from a synchronous evolved node B or received through a GPS reception module, the devices are inevitably required to access the synchronous evolved node B or the GPS reception module. However, some communication schemes provided by communication providers may not support a synchronous evolved node B. In such cases, it may be impossible to set synchronization between devices by using time information received from a synchronous evolved node B. Further, when a device is located in a GPS shaded area (i.e., an area with poor GPS reception, such as an area between high-story buildings, an area within a tunnel, an indoor area of a building, etc.), the device may be unable to receive time information from a GPS and be thus unable to set synchronization between devices. Eventually, when a device is unable to smoothly access a synchronous evolved node B or a GPS reception module as described above, the device is unable to start the D2D communication.